This invention relates generally to test apparatus for determining the properties of materials, and more particularly to a continuous-flow moisture tester for measuring the moisture content of materials such as agricultural products being conveyed therethrough.
In the past moisture testers of the continuous flow variety have been adapted for measuring moisture content of granular material such as agricultural grains. Such moisture testers have included, for example, a test cell comprising a pair of parallel plates that function as a capacitor, the material to be tested being discharged from a chute and falling by gravity between the plates. Another prior art tester utilizes a test cell having cylindrical, coaxial electrodes, an enclosed top, an open bottom and upper side-wall exit apertures. This tester also includes a conveyor screw for forcing material to be tested upwardly through the open bottom of the test cell. A further prior art tester utilizes an open-ended test cell having inner and outer coaxial, cylindrical electrodes that have their axis vertical during use. In the latter coaxial electrode arrangement, it is necessary to provide a plurality of supporting cross rod members to support and hold the inner electrode coaxially within the outer electrode.
A common problem encountered in the foregoing arrangements is that of maintaining a substantially even and constant flow of material through the test cell, while keeping the cell substantially evenly filled with material to be tested. For example, it will be appreciated that the parallel plate arrangement presents a geometry difficult to keep evenly filled with flowing material. Moreover, when agricultural grains such as wheat, corn or the like are being tested, the side-wall exit apertures and the cross rods in the respective described coaxial electrode arrangements tend to collect foreign materials such as husks, stalks and the like, thereby causing voids in the grain flow and subsequent inaccuracies in moisture measurements taken thereform. Further, plugging up of the test cell and loss of flow therethrough often occurs in both prior art arrangements. Additionally, certain of the foregoing types of moisture testers, while useful and generally quite successful when used with readily flowing materials such as wheat or corn, exhibit further aggravation of the above-noted problems when less readily flowing materials are sought to be tested thereby. For example, in the case of relatively low density, fine ground materials such as hominy feed, fish meal, cotton seed meal, prepelletized formula feed and the like, the material tends to bridge over and obstruct any restricted areas. Such areas may be in the cell, or in attached outlet devices, such as restrictor cones, commonly used with such moisture testers. Further, in the testing of bulkier fibrous materials such as chopped alfalfa, bermuda grass or the like, the foregoing problems become even more acute.
A related problem encountered in the foregoing types of prior art moisture testers is obtaining a reliable continuous moisture measurement of materials flowing therethrough, substantially unaffected by the difference in densities of different materials to be tested, as well as by variations in the density of a given material being tested. The prior art devices rely primarily upon various physical arrangements for attempting to maintain material at a constant predetermined density as it flows through the test cell. It will be apparent, however, that such arrangements may have problems in view of the plugging and voiding discussed above, and in view of the natural variations in density within a given batch of material being tested.